The present invention is generally directed to toner processes, and more specifically, to coalescence processes for the preparation of toner compositions. In embodiments, the present invention is directed to the economical preparation of toners without the utilization of the known pulverization and/or classification methods, and wherein toners with an average volume diameter of from about 1 to about 25, and preferably from 3 to about 14 microns, and narrow GSD characteristics can be obtained. The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes, and lighography. In embodiments, the present invention is directed to in situ processes for recycling toner fines, that is, for example, the use of classified toner materials obtained from conventional process, like melt blending, wherein the average particle volume diameter of the toner particles is from about 0.01 and preferably to about 7 microns. In one embodiment, the present invention is directed to in situ processes for preparing toners by first dispersing toner fines in an aqueous solution containing an ionic surfactant and nonionic surfactant by utilizing, for example, a high shearing device, such as a Branson 750 Ultrasonifyer or Brinkman Polytron, adding thereto a counterionic surfactant with a polarity opposite to that of the ionic aqueous surfactant resulting in a flocculation or heterocoagulation, and shearing the mixture thereafter for an effective period of time of, for example, from about 1 minute to about 10 minutes, followed by stirring for an induction period of from, for example, about 5 minutes to about 3 days and heating the mixture above the glass transition temperature, such as from about 10.degree. C. to about 50.degree. C. above the glass transition temperature of the resin, to cause coalescence of the toner fine particles and provide toner particles of, for example, from about 7 microns to about 21 microns in average volume diameter. In another embodiment thereof, the present invention is directed to an in situ process comprised of first dispersing fine toner particles of average volume diameter of from about 1 micron to about 5 microns, and comprised of, for example, a pigment such as carbon black, HELIOGEN BLUE.TM. or HOSTAPERM PINK.TM. of from about 2 to about 10 percent by weight of toner, a resin such as styrene butadiene or styrene methacrylate of from about 70 to about 97 percent by weight of the toner and optional charge control agent of from about 0.1 to about 3 percent by weight of the toner in an aqueous mixture containing a cationic surfactant, such as MIRAPOL.TM. or SANIZOL B-50.TM., and nonionic surfactant such as IGEPAL 897.TM., utilizing a high shearing device, such as Branson 750 ultrasonicator or a Brinkman Polytron, or microfluidizer or sonicator, thereafter adding an anionic surfactant such as sodium dodecyl sulfate or NEOGEN R.TM., thereby resulting in a flocculation or heterocoagulation of the fine toner particles, and which on further shearing of from about 1 minute to about 120 minutes followed by mechanical stirring of from about 1 minute to about 3 days results in the redispersion of the fine toner particles; and thereafter heating to provide for fine toner particle fusion or coalescence; followed by washing with, for example, hot water to remove surfactant, and drying whereby toner particles comprised of resin and pigment with various particle size diameters can be obtained, such as from about 5 to about 21 microns in average volume particle diameter. The aforementioned toners are especially useful for the development of colored images with excellent line and solid resolution, and wherein substantially no background deposits are present. While not being desired to be limited by theory, it is believed that the flocculation or heterocoagulation is formed by the neutralization of the cationic surfactant absorbed on the toner particles, with the anionic surfactant added during shearing step. The high shearing stage disperses the formed large flocculants to a dispersed mixture of fine toner particles. Thereafter, heating is applied to fuse the fine toner particles or coalesce the fine particles to toner composites. Furthermore, in other embodiments the ionic surfactants addition can be changed, such that the fine toner particles are first dispersed in an aqueous solution containing the anionic surfactant, and the cationic surfactant is added thereafter, followed by shearing, stirring and heating to provide toner particles by fusion or coalescence of the fine toner particle to toner size particles of from about 7 to about 21 microns in average volume diameter as measured by the Coulter Counter. In embodiments, the toner composite morphology can be controlled such that a potato shape is attained by heating the statically bounded aggregate particle of from about 10.degree. to about 20.degree. C. above the glass transition temperature of the resin, which is generally from about 50.degree. to about 65.degree. C., or alternatively can be controlled such that a spherical shape is attained by heating the statically bounded aggregate particles to from about 20.degree. to about 40.degree. C. above the glass transition temperature of the resin.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with an average volume particle diameter of from about 7 microns to about 20 microns and with broad geometric size distribution of from about 1.4 to about 1.7. In such processes, it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.4 are attained. However, in the aforementioned conventional process, low toner yields after classification may be obtained. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. The classified portions, which are from about 15 to about 30 percent by weight of the toner, are of average volume diameter of from about 5 to about 9 microns as measured by a Coulter Counter. This classified portion is usually recycled in the extrusion or melt kneading step, or disposed in acceptable land filled sites. Moreover, during the preparation of smaller sized toners with particle sizes of from about 7 microns to about 11 microns, lower toner yields are obtained after classification, such as from about 50 percent to about 60 percent after classification, and the classified portion is from about 40 to about 50 percent by weight of toner of average volume diameter of from about 1 to about 5 microns as measured by the Coulter Counter. This classified portion is usually recycled in the melt kneaded or extrusion steps. With the processes of the present invention, in embodiments the classified portion is referred to as fine toner particles, and of from, for example, about 2 microns to about 5 microns in average diameter can be recycled in a more economical manner without resorting to conventional process such as melt kneading or extruding, micronizing and pulverizing. With the process of this invention, the toner fines can be recycled to provide toners of from about 7 to about 21 microns as determined by the Coulter Counter and with geometric size distributions, such as from about 1.20 to about 1.4, and preferably from about 1.20 to about 1.35. High toner yields are attained, such as from about 90 percent to about 98 percent, in embodiments of the present invention.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of this '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, note column 9, lines 50 to 55, wherein a polar monomer such as acrylic acid in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group, see Comparative Example I. The process of the present invention need not utilize polymers with polar acid groups, and toners can be prepared with resins such as poly(styrene butadiene) or PLIOTONE.TM. without containing polar acid groups. Additionally, the toner of the '127 patent does not utilize, it is believed, counterionic surfactant and flocculation process. In U.S. Pat. No. 4,983,488, there is disclosed a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. This process is thus directed, for example, to the use of coagulants, such as inorganic magnesium sulfate, which are not easily removed from the toner product. Furthermore, the '488 patent does not disclose the use of counterionic flocculation. Similarly, the aforementioned disadvantages are noted in other prior art, such as U.S. Pat. No. 4,797,339, wherein there is disclosed a process for the preparation of toners by resin emulsion polymerization, which similar to the '127 patent utilizes polar resins of opposite charges, and wherein flocculation as in the present invention is not disclosed; and U.S. Pat. No. 4,558,108, wherein there is disclosed a process for the preparation of a copolymer of styrene and butadiene by specific suspension polymerization.
In copending application U.S. Ser. No. 921,165, the disclosure of which is totally incorporated herein by reference, there is disclosed a process for the preparation of toners comprised of dispersing a polymer solution comprised of an organic solvent, and a polyester homogenizing and heating the mixture to remove the solvent and permit formation of the toner composites. Additionally, there is disclosed in U.S. Pat. No. 5,278,020, the disclosure of which is totally incorporated herein by reference, a process for the preparation of in situ toners comprising a halogenization procedure which chlorinates the outer surface of the toner which results in enhanced blocking properties. More spefifically, this patent application discloses an aggregation process wherein a pigment mixture containing an ionic surfactant is added to a resin mixture containing a polymer resin particles of less than 1 micron nonionic and counterionic surfactant, and thereby causing a flocculation which is dispersed to statically bound aggregates of about 0.5 to about 5 microns in volume diameter as measured by the Coulter Counter, and thereafter heating to form toner composites of from about 3 to about 7 microns in volume diameter and narrow geometric size distribution of from about 1.2 to about 1.4, as measured by the Coulter Counter, and which apparently exhibit low fixing temperature of from about 125.degree. to about 150.degree. C., low paper curling, and image to paper gloss matching.